"I thought the situation was that Governor Blagojevich got a huge campaign contribution from the union, and virtually as soon as he got into office he took out his pen and signed an executive order that had the effect of putting, what was it, $3.6 million into the union coffers?"

But Illinois Attorney Lisa Madigan, whose office argued the case against Harris, said the state has a compelling interest in promoting union representation of these workers.

"What the state of Illinois has had to do, as you heard during the argument, is find a mix of benefits so we're able to attract and retain a high-quality workforce," she said. "And quite frankly, before there was an exclusive representative engaged in collective bargaining, that was not the case in Illinois."

Between 2002 and 2012 Madigan received $779,773 in campaign donations from government worker unions, including $129,000 from the SEIU.

The court's four more liberal justices appeared to oppose changing the law.

If the court were to do so, Justice Stephen Breyer said, it would overturn 35 years of established legal precedent.

On the other hand, some of the more conservative members of the court - Chief Justice John Roberts, Alito and Justice Anthony Kennedy - appeared ready to side with Harris and the others who brought the lawsuit.

Justice Clarence Thomas did not ask questions during oral arguments, which is his practice.

That leaves Scalia, usually a stalwart conservative, as the potential swing vote on what seems to be a case centered on freedom of speech.

Workers who refuse to join a union are often charged a "representation fee," which is supposed to cover the cost of things like collective bargaining but not union political activities.

Kennedy noted that defining what is and isn't political activity is difficult. For example, he said collective bargaining for government workers affects the size of government - something that has political implications "in an era where government is getting bigger and bigger, and this is becoming more and more of an important issue to more people."

Page 2 of 2 - If the court finds in Harris' favor, public-sector labor unions could be weakened, Harvard Law School professor Benjamin Sachs, an expert on labor law and a former SEIU attorney, said in an interview last week.

If the court issues a narrow ruling, it could say that home care workers are not state workers and can't be compelled to give money to a union. This would deprive unions of a significant amount of revenue that they are receiving.

In fact, some justices expressed skepticism about whether these workers, many of whom are caring for relatives, really meet the definition of state employees.

The court is expected to rule on the case this summer.

Harris doesn't consider herself a state employee, just a mother looking after her son.

"I'm only doing this because it's the right thing for Josh. I didn't want - I didn't seek out - publicity or to become the face of changing public-sector unions. I just really wanted to do what was right for Josh."